Currently, 3rd generation cellular communication systems are being rolled out to further enhance the communication services provided to mobile phone users. The most widely adopted 3rd generation communication systems are based on Code Division Multiple Access (CDMA) and Frequency Division Duplex (FDD) or Time Division Duplex (TDD) technology.
TDD provides for the same carrier frequency to be used for both uplink transmissions, i.e. transmissions from the mobile wireless communication unit (often referred to as wireless subscriber communication unit) to the communication infrastructure via a wireless serving base station as well as downlink transmissions, i.e. transmissions from the communication infrastructure to the mobile wireless communication unit via a serving base station. In TDD, the carrier frequency is subdivided in the time domain into a series of timeslots. The single carrier frequency is assigned to uplink transmissions during some timeslots and to downlink transmissions during other timeslots. An example of a communication system using this principle is the Universal Mobile Telecommunication System (UMTS). Further description of CDMA, and specifically of the Wideband CDMA (WCDMA) mode of UMTS, can be found in ‘WCDMA for UMTS’, Harri Holma (editor), Antti Toskala (Editor), Wiley & Sons, 2001, ISBN 0471486876.
In order to provide enhanced communication services, the 3rd generation cellular communication systems are designed to support a variety of different and enhanced services. One such enhanced service is multimedia services. The demand for multimedia services that can be received via mobile phones and other handheld devices is set to grow rapidly over the next few years. Multimedia services, due to the nature of the data content that is to be communicated, require a high bandwidth. Hence, packet-switched based data provision is generally adopted.
Typically, subscriber units (referred to as User Equipment (UE) in 3GPP parlance) that are operationally inactive are placed in a ‘paging’ state. In this ‘paging’ state UEs very occasionally listen (possibly less frequently than 500 msec's) to a dedicated paging channel, which carries messages that indicate whether there is downlink (DL) data for the UE. If the message indicates that DL data exists for the UE, the UE knows that it should transition into an operational state, such as a ‘data traffic’ state, where it can send and receive data traffic. If there is UL traffic to be sent to the network, then the UE transitions straight away into the appropriate state to send data traffic. However, it is known that this state transition can take a substantial period of time (typically the state transition can be in the order of 100 msec).
The paging channel is deliberately designed so that the UE only has to ‘infrequently’ access it to receive messages, in order to minimise the power requirements of the UE. However, in accessing the paging channel infrequently, thereby saving power, there is a consequent increase in latency in subsequently transmitting or receiving data. In a packet switched based cellular communication system this latency may be severely detrimental to the overall performance of the system.
Once the UE has been successfully paged, and is in the ‘data traffic’ state, the UEs listens, in every frame, to an allocation channel that allocates resources on a separate shared channel for a limited period of time.
The allocation of shared resources may be performed either in response to the UE signaling to the network that it has uplink (UL) buffer occupancy, i.e. the UE has buffered data that it needs to transmit to the network on an uplink channel, or through provision of internal reporting within the network in the case of downlink (DL) data. Supporting UE signaling and/or internal reporting of DL data adds further complexity to the system.
It would of course be possible to keep as many users in the ‘data traffic state’ as possible even though they had not sent or received data for a long period of time. This would minimise latency. However, it would be detrimental to power requirements at the UE because it would have to listen to the allocation channel in every frame.
It is shown, therefore, that there is trade-off between minimizing UE power requirements and latency performance.
Subsequently, in the ‘data traffic’ state, all UEs listen, in every frame, to an allocation channel that allocates shared resources for a limited period of time. Thus, the requirement for all UEs to listen in every frame to an allocation channel, before transitioning to an allocated channel from a plurality of shared resources, as instructed by the network, also increases the latency.
Consequently, current techniques are suboptimal. Hence, an improved mechanism to address the latency versus power saving problem of in packet switched cellular communication systems is desired.